Process of making cyanids.



UNITED STATES Patented June 13, 1905.

PATENT QFFIQE.

GROSSMANN CYANIDE PATENTS SYNDICATE CHESTER, ENGLAND.

LIMITED, OF MAN- PROCESS OF MAKING CYANIDS.

SPECIFICATION forming part of Letters Patent No. 792,261, dated June 18, 1905. Application filed February 7, 1905. Serial No. 244,674.

To all whom it may concern.-

Be it known that I, JAooB GROSSMANN, a' citizen of Great Britain, residing at Harpurhey, Manchester, in the county of Lancaster, England, have invented certain new and useful Improvements in and Connected with the Manufacture of Cyanids, of which the following is a full, clear, and exact description.

The object of this invention is to prepare alkaline cyanids from ferrocyanids. An invention for a somewhat similar purpose is the subject of an application, Serial N 0. 152,952, filed April 16, 1903, for Letters Patent for improvements in and connected with the manufacture of cyanids. In that application I have shown that the hydrocyanic acid given off by distilling a ferrocyanid with a mineral acid is absorbed in caustic alkali, from which solution a solid alkaline cyanid is obtained by boiling down. I have found that the same result can be attained by absorbing the hydrocyanic acid in milk of lime or another hydrate of an alkaline earth, such as barium or strontium hydrate, and decomposing the cyanid obtained with an alkaline sulfate. However, that process could never become a commercial success unless the metal ferro ferrocyanid which is ob; tained by the decomposition of ferrocyanids with mineral acids is quantitatively reconverted into ferrocyanid, and for that reason the process just described must be combined with that specified in the application men tioned above, Serial N 0. 152,952, in which the quantitative reconversion of the metal ferroferrocyanid into ferrocyanid is brought about by boiling with caustic alkali in the presence of air in excess. It will therefore be understood that the present invention forms a combination of two processes-viz., the mutual decomposition of the calcium cyanid formed with alkali sulfate and the quantitative reconversion of the metal ferroferrocyanid obtained in the distillation of ferrocyanids with mineral acids.

The process for making alkaline cyanids according to the present invention comprises a combination of the following operations: first, distillation of hydrocyanic acid second, absorption of the hydrocyanic acid and further treatment of the resulting cyanid solution third, reconversion of the metal ferro-ferrocyanid. These operations are carried on on a large scale as follows:

First. Distillafion of hydrocycmic acid-I have found that lead is not acted on either by the mixture of ferrocyanid and sulfuric acid or by hydrocyanic acid, and I therefore prefer to carry out this operation in a still made of lead but enameled iron or other suitable material may be used for its constructionwhen it is advisable to do so. Separate pipes for the supply of live steam, air,- sulfuric acid, and ferrocyanid solution go to the bottom of the still, which may also contain a steam-coil for heating by confined steam. It is connected at the top with a dephlegmating or fractionating apparatus, which may be cooled by water, cold air, or otherwise. I have found that the vapor of hydrocyanic acid does not act on iron, and the dephlegmating arrangement may therefore be made of that material. Pipes lead from the dephlegmating apparatus to a number of absorbing vessels made of iron or other suitable material and fitted with suitable agitating machinery. The whole system is at its outlet connected with a Korting exhauster or similar apparatus for producing a partial vacuum or for drawing air through under a partial vacuum or otherwise. A suitable form of apparatus is illustrated in the specification forming the subject of an application, Serial No. 152,952, filed April 16, 1903.

When an operation is commencing, the necessary quantity of the saturated solution of ferrocyanid of potash, containing about twenty-five per cent. of crystallized ferrocyanid, is run into the still, (which is still hot from a previous operation) all the taps are closed, and the eXhauster is set to work, so as to keep up a partial vacuum of about four inches of mercury. The taps for live and confined steam are then turned on and the acid, which contains about twenty-five per cent. II,SO is run in slowly at the rate of about one gallon per minute or slower. The quantity of acid used is about two to five per cent.

in excess of the quantity necessary to "form the three molecules of neutral potassium sulfate, corresponding to two molecules of ferrocyanid. The apparatus works very regularly, and when once it has been ascertained how long it takes to finish an operation it will be found that subsequent operations under the same conditions will finishv in the same time. The ferrocyanid used should be reasonably free from carbonates, sulfids, and. other ingredients which may either interfere with the reaction in the still or influence the quality of cyanid produced.

Several stills supplied with overflows and suitably connected may be combined in such a manner as to work continuously;

During part or the whole of the operation a current of air, heated or otherwise, may be passed through the still.

Second. Absorption ofthc hydrocr tmic acid (mdjitrther treatment of the resulting cq a/rrid s0Zut'Z0n.-The absorption vessels are closed boxes or pots made of iron or other suitable material, fitted with agitating machinery and of such size that they will hold suflicient milk of lime to absorb the hydrocyanic acid and the vapors evolved from four or more still operations. Two, three, or more of these vessels are arranged in series, preferably at increasing heights, so that the liquid from the higher can be drawn into the lower vessel. The hydrocyanic acid enters the lowest ves sel first, is taken to the bottom, the gas leaves through a pipe at the top, and is drawn through the box or boxes at a higher level in the same manner. The boxes are charged with milk of lime, to which an alkaline sulfate is added. After one or several still operations further quantities of lime and sulfate, the latter either in concentrated solution or in the solid state, may be added. The temperature is regulated by cooling the absorption-pots. It is advisable to keep it below 40 eentigrade. hen the first absorbing vessel sufliciently saturated with hydrocyanic acid, which is as certained by test, its contents are run off into suitable covered tanks, and the pot may be recharged. The resulting mass chiefly consists of a mixture of an alkaline cyanid and calcium sulfate. It is allowed to settle in closed vessels, guarded against access of air and light, and the liquor separated from the precipitate by decantation and the latter washed, or the filtration and washing may be carried out by means of a centrifugalmachine or a filter-press. The resulting liquor may be purified. by the addition of alkaline carbonates or by any other means well known and apparent to chemists. The liquors, purified or otherwise, obtained by either of the above means may be concentrated or made into solid by boiling down in. a suitable vacuumpan. Care should be taken that no calcium cyanid as such may be conveyed to the vacuum-pan or may form in the process of evapo ration.

Third. Rccomrcrston of the metalji'rro fhrrocr rmid lhe contents of the still after the distillation is finished are run into tanks and the solution of alkali sulfate separated from the metal 'ferro-ferrocyanid by decantation or filtration. The alkali sulfate, which is slightly acid, is neutralized by means of calcium carbonate, alkali carbonate, or other suitable means and may then be further purified and afterward concentrated by boiling down, crystallizing, or fishing. The metal ferro-ferrocyanid, which need not be quite free from sulfate, is made neutral by means of alkalicarbon ate or caustic alkali and mixed with the equivalent quantity plus about five per cent. of caustic soda or potash or its carbonates, or a mixture of both. It is then heatedin suitable vessels and of such capacity as will contain the large quantity of froth which is produced during the operation either by steam or other means to boiling, violently agitated, and air passed through by means of a compressor or steamrinjector until a test shows that all the metal ferro ferrocyanid has been decomposed. The air may be heated or otherwise. WVith some experience the time necessary for this can be fixed approximately for each operation after a few trials. The colorof the precipitate of iron produced should be brownish-black when the operation is finished. The resulting solution of alkali ferrocyanid may be separated from the iron compound by decantation or filtration and the latter washed free from ferrocyanid. The resulting ferrocyanid solution is carefully neutralized with a suitable acid or by other means and may go back into the process either as solution or may be further concentrated or boiled down and crystallized.

Instead of sulfuric acid. suitable acid. sulfates such as sodium or potassium bisul'fate, niter-cake, or similar compoundsmay be used.

I have so far confined myself to the action of sulfuric acid on ferrocyanid, being the most practicable form of my process, in so far as it enables me to use lead for the distilling apparatus and to recover the alkali con tained in the original ferrocyanid as sulfate, which can. be made available as described above; but it is well known that if hydrochloric, phosphoric, of similar acids are used hydrocyanic acid. and metal 'ferro-'ferrocy anid are produced, and I have found that practically the reaction takes place in the same way as with sulfuric acid and that with hydrochloric, phosphoric, and similar acids whatever the yield of hydrocyanic acid the resulting metal ferro-ferrocyanid contains exactly the amount of cyanogen corresponding to the difference between the total cyanogen originally contained in the ferrocyanid ITO ing the insoluble residue of metal ferro-ferrocyanid obtained by the decomposition of fcrrocyanids with acids, into fcrrocyanid by boiling with a caustic alkali in the presence of air in excess, substantially as described.

In testimony whereof I have signed my name to this specification in the presence of 20 two subscribing witnesses.

JACOB GROSSMAN N WVitnesses:

THoMAs A. ANDREWS, i G. E. BANNISTER. 

